1. Field of the Invention
The invention relates to a tilt detecting method in a recorded information reproducing apparatus for detecting a tilt occurring between a recording disk as a recording medium and a pickup to read recorded information from the recording disk.
2. Description of Related Art
To accurately read out recorded information from an optical disk as a recording medium, it is necessary to irradiate a reading beam perpendicularly to the recording surface of the optical disk. However, if the optical disk is warped, the reading beam cannot be irradiated perpendicularly to the recording surface of the optical disk and information reading precision deteriorates.
In recorded information reproducing apparatuses for reproducing the recorded information from the optical disk, a tilt sensor to detect a tilt occurring between the recording disk and the pickup is provided. In such an arrangement, the whole pickup is inclined by an angle corresponding to the tilt detected by the tilt sensor or a desired signal process according to the tilt is performed to the read signal which was read out by the pickup, thereby suppressing the deterioration in information reading precision.
FIG. 1 is a diagram schematically showing a construction in which a tilt sensor 4 is provided in a recorded information reproducing apparatus, to detect a tilt occurring between the recording disk and the pickup as mentioned above.
In FIG. 1, a beam generator 41 in the tilt sensor 4 irradiates divergent light which is irradiated to two different positions on the recording surface of a recording disk 3 which is rotated by a spindle motor 2. A photodetector 42 receives a part of the reflection light when the divergent light is irradiated to the recording surface of the recording disk 3 and supplies a first detection signal having a level according to a photosensitive amount to a subtractor 44. A photodetector 43 is arranged at a position that is symmetrical to the photodetector 42 around the beam generator 41 as a center. The photodetector 43 receives a part of the reflection light when the divergent light is irradiated to the recording surface of the recording disk 3 and supplies a second detection signal having a level according to a photosensitive amount to the subtractor 44. The subtractor 44 obtains a level difference between the first and second detection signals and outputs as a tilt error signal. It is now assumed that each of the beam generator 41 and photodetectors 42 and 43 is arranged on the same parallel plane as that of a pickup (not shown).
Now, if we assume that a parallel relation is maintained between the recording surface of the recording disk 3 and the pickup, since the amounts of reflection light which is received by the photodetectors 42 and 43 are the same, a tilt error signal become equal to "0". If a warp or the like exists in the recording disk 3, the amounts of reflection light which is received by the photodetectors 42 and 43 are different, so that a tilt error signal corresponding to a difference between the reflection light amounts is generated.
If the tilt sensor 4 is provided in the recorded information reproducing apparatus, there however arises a problem that the scale of the apparatus becomes large. Furthermore, upon installation of the tilt sensor in the reproducing apparatus, the tilt sensor 4 has to be accurately attached at the position where the parallel relation between the disk and the pickup is held, so that there is a problem such that high attaching precision is required.